Method of manufacturing an electronic circuit formed on a substrate

ABSTRACT

An image forming apparatus comprises an exposure unit forming an electrostatic latent image on a photo conductor based on image information, a developing unit developing the electrostatic latent image by toner made of formation material of a circuitry layer, and an electrostatic transferring unit transferring a toner image on the photo conductor onto a substrate. The toner image is transferred so as to cover at least a part of a conductor layer formed on the substrate. At this time, excessive charges caused in the conductor layer accompanying the start of the transfer of the toner image are removed. Alternatively, charges of which polarity is reverse to that of the toner are added to the conductor layer. These allow the circuitry layer to be formed to have a desired pattern favorably and securely on the conductor layer.

CROSS-REFERENCE TO THE INVENTION

This is a division of application Ser. No. 11/100,388, now U.S. Pat. No.7,433,637, filed Apr. 7, 2005, which is incorporated herein byreference.

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2004-114059 filed on Apr. 8,2004, Japanese Patent Application No. 2004-115795 filed on Apr. 9, 2004,and Japanese Patent Application No. 2004-163408 filed on Jun. 1, 2004;the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus to which anelectrophotographic system is applied, and a method of manufacturing anelectronic circuit using the same.

2. Description of the Related Art

Conventionally, etching and screen printing methods have been heavilyused in forming an electronic circuit applied to a wiring board,semiconductor element and the like. When the etching method is used toform a conductor pattern, exposure masks are necessary for respectivelayers. In the screen printing method, exclusive masks are necessary aswell. Since tremendous amounts of money and time are required indesigning and manufacturing these masks, manufacturing cost andmanufacturing time of the electronic circuit are affected significantly.In order to solve such problems of the conventional methods, the methodof forming the conductor pattern and the like by using anelectrophotographic system has been developed (refer to Japanese PatentLaid-open Application No. Hei 7-263841, Japanese Patent Laid-openApplication No. 2001-284769, for example).

The conductor pattern to which the electrophotographic system is appliedis formed as follows, for example. First, toner (charged particles)which contains metal fine particles in insulating resin particles madeof thermosetting resin such as epoxy resin is used to selectively form aplating base layer on a substrate. This plating base layer is subjectedto electroless plating, whereby a metal conductor layer having a desiredcircuit pattern is formed (refer to Japanese Patent ApplicationLaid-open No. 2004-048030, for example). The electrophotographic systemis also applied to the formation of an insulating layer. The insulatinglayer is formed by bringing the toner made of the insulating resinparticles into adhesion onto the substrate, and thermally fixing thisinsulating resin particle layer.

An image forming apparatus used in manufacturing the electronic circuitis mainly constituted of an exposure unit forming an electrostaticlatent image on a photo conductive drum, a developing unit bringing thetoner into adhesion with the electrostatic latent image to form avisible image, a transferring unit transferring the visible image by thetoner (toner image) onto the substrate, and a fixing unit fixing thetoner image transferred onto the substrate. Although several methods,such as an electrostatic transfer method, pressure transfer method,adhesive transfer method and the like, are known as the method oftransferring the toner image formed on the surface of the photoconductive drum onto the substrate, the electrostatic transfer methodwhich is suitable for high speed and whose structure is relativelysimple is heavily used in general copying machines, laser printers andthe like.

The electrostatic transfer method is the method of transferring thetoner image formed on the surface of a photo conductor onto thesubstrate by electrostatic force. When negative-charged toner istransferred from the surface of the photo conductor onto the substrate,for example, a voltage is applied between the photo conductor and thesubstrate so that positive charges whose polarity is reverse to that ofthe toner are added to the back face side of the substrate. Bygenerating an electric field between the photo conductor and thesubstrate based on the application of the voltage, the negative-chargedtoner is moved from the surface of the photo conductor onto thesubstrate by the electrostatic force. Thus, the toner image formed onthe surface of the photo conductor is electrostatically transferred ontothe substrate.

When the electronic circuit is manufactured using theelectrophotographic system, it is essential that the insulating layer isformed on the metal conductor layer using the insulating resin particlesas the toner. When the electrostatic transfer method is applied toformation process of the insulating layer using the insulating resinparticles, the problem is caused that the transfer of the insulatingresin particles (toner) onto the metal conductor layer is performed lesssufficiently toward the rear side in the moving direction of thesubstrate. Namely, although the insulating resin particles aretransferred comparatively well on the front side in the moving directionof the metal conductor layer, the insulating resin particles cease to betransferred from the middle of the metal conductor layer and only thedefective insulating layer is obtain able. This is supposed to be causedby an electrostatic induction phenomenon of the conductor by theelectric field.

Further, when the electrophotographic system is applied to the formationof the insulating layer, it is necessary to form the insulating layer tohave a desired pattern with high accuracy on the conductor layer havingvarious circuit patterns. However, since the conventional image formingapparatus has low accuracy of positioning of respective patterns, it hasthe problem that accuracy of form and the like of the electronic circuittend to lower. The electrophotographic system is also applied to themanufacturing of a wiring board having multilayer wiring structure. Thewiring board having the multilayer wiring structure is manufactured bylayering the conductor layers and insulating layers for plural times. Insuch a case, the positioning of the respective patterns becomes furtherdifficult.

In formation process of the conductor layer to which theelectrophotographic system is applied, the plating base layer is formedusing the toner containing the metal particles in the insulating resinparticles, as described above. The toner containing the metal particleshas low electrical resistance, and is difficult to control the amount ofcharges as compared to normal toner for electrophotography.Additionally, the thermosetting resin such as epoxy resin whichconstitutes the metal particle-containing toner has more functionalgroups as compared to thermoplastic resin such as styrene resin andpolyester resin which are used for the normal toner forelectrophotography. It is therefore difficult to maintain the amount ofcharges especially in a high-humidity environment because of moistureabsorption.

Under the condition where the electrical resistance of the toner is lowand the amount of charges is decreased, the phenomenon in which thetoner adheres to the parts without the electrostatic latent image on thephoto conductor, that is, the so-called “fog” tends to be caused. Whenthe “fog” is caused, the toner adheres to the parts other than thedeveloped circuit pattern, whereby the problems such as a short circuitare caused in the circuit by the conductor layer. This results in lowerreliability and a lower manufacturing yield of the electronic circuitwhich is applied to the wiring board and the like.

As described thus far, the manufacturing process of the electroniccircuit using the conventional image forming apparatus has the problemthat defective shapes of the respective layers constituting theelectronic circuit, such as transfer failure of the insulating layer andthe like, positioning failure of the respective layers, the fog informing the conductor layer (plating base layer) and the like, tend tobe caused. The transfer failure due to the electrostatic inductionphenomenon of the conductor is not limited to the insulating layer. Thetransfer failure may be caused similarly when the electrophotographicsystem is applied to the formation of a semiconductor layer, forexample, depending on the magnitude of the electric field to be applied.Accordingly, the technique of forming the respective layers constitutingthe electronic circuit to have desired patterns favorably and securelyis required.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an image formingapparatus and a method of manufacturing an electronic circuit which makeit possible to prevent defective shapes of respective layersconstituting the electronic circuit. Moreover, it is an object of thepresent invention to provide the image forming apparatus and the methodof manufacturing the electric circuit which can form a circuitry layerhaving a desired pattern favorably and securely, informing the circuitrylayer such as an insulating layer, semiconductor layer and the like on aconductor layer using an electrophotographic system. It is anotherobject of the present invention to provide the image forming apparatusand the method of manufacturing the electric circuit which prevent thephenomenon in which toner adheres to parts without an electrostaticlatent image (fog) to form a clear conductor pattern with highreproducibility, in forming the conductor pattern on a substrate usingthe electrophotographic system. It is still another object of thepresent invention to provide the image forming apparatus and the methodof manufacturing the electric circuit which can enhance accuracy ofposition of the circuitry layer, in forming the circuitry layer on thesubstrate using the electrophotographic system.

According to a mode of the present invention, an image forming apparatusforming an image on a substrate having a conductor layer, using tonercontaining formation material of a circuitry layer, comprises a photoconductor, an exposure unit exposing the photo conductor based on imageinformation of the circuitry layer to form an electrostatic latent imageon the photo conductor, a developing unit developing the electrostaticlatent image on the photo conductor by the toner to form a toner imageon the photo conductor, an electrostatic transferring unit transferringthe toner image on the photo conductor onto the substrate so that atleast a part of the conductor layer is covered with the toner image, anda charge removing unit arranged to be in electrical contact with atleast a part of an exposed face of the conductor layer to removeexcessive charges caused in the conductor layer accompanying the startof the transfer of the toner image.

According to another mode of the present invention, an image formingapparatus forming an image on a substrate having a conductor layer,using toner containing formation material of a circuitry layer,comprises a photo conductor, an exposure unit exposing the photoconductor based on image information of the circuitry layer to form anelectrostatic latent image on the photo conductor, a developing unitdeveloping the electrostatic latent image on the photo conductor by thetoner to form a toner image on the photo conductor, an electrostatictransferring unit transferring the toner image on the photo conductoronto the substrate so that at least a part of the conductor layer iscovered with the toner image, and a bias voltage applying unit arrangedto be in electrical contact with at least a part of an exposed face ofthe conductor layer to add charges of which polarity is reverse to thatof the toner to the conductor layer.

According to still another mode of the present invention, an imageforming apparatus forming an image on a substrate using toner containingmetal particles, comprises a photo conductor, a charging unit chargingthe photo conductor, an exposure unit exposing the photo conductor whichis charged in the charging unit, based on image information, adeveloping unit developing the photo conductor which is exposed in theexposure unit, using the toner, a controlling unit controlling anabsolute value of white contrast of the photo conductor to 200 V orlower, when developing the photo conductor in the developing unit, and atransferring unit transferring a toner image, which is formed on thephoto conductor in the developing unit, onto the substrate.

According to yet another mode of the present invention, an image formingapparatus forming an image on a substrate, comprises a photo conductor,an exposure unit exposing the photo conductor based on image informationto form an electrostatic latent image on the photo conductor, adeveloping unit developing the electrostatic latent image on the photoconductor by toner to form a toner image on the photo conductor, atransferring unit transferring the toner image on the photo conductoronto the substrate, a substrate carrier unit comprising a positioningmeans to mount the substrate on a predetermined position and a referencemarker to show the position of the substrate to be carried, to carry thesubstrate so that the substrate moves between the photo conductor andthe transferring unit, a detecting unit detecting the passage of thereference marker, and a controlling unit allowing the exposure unit tostart exposure of the photo conductor, by taking time when the detectingunit detects the passage of the reference marker as a reference.

According to still another mode of the present invention, an imageforming apparatus forming an image on a substrate, comprises a firstimage forming unit comprising a first photo conductor, a first exposureunit exposing the first photo conductor based on image information toform an electrostatic latent image on the first photo conductor, a firstdeveloping unit developing the electrostatic latent image on the firstphoto conductor by metal particle-containing toner to form a toner imageon the first photo conductor, and a first transferring unit transferringthe toner image on the first photo conductor onto the substrate, asecond image forming unit comprising a second photo conductor, a secondexposure unit exposing the second photo conductor based on imageinformation to form an electrostatic latent image on the second photoconductor, a second developing unit developing the electrostatic latentimage on the second photo conductor by toner for forming an insulatinglayer to form a toner image on the second photo conductor, and a secondtransferring unit transferring the toner image on the second photoconductor onto the substrate, a substrate carrier unit comprising apositioning means to mount the substrate on a predetermined position anda reference marker to show the position of the substrate to be carried,to carry the substrate so that the substrate moves between the firstphoto conductor and the first transferring unit and between the secondphoto conductor and the second transferring unit, a detecting unitdetecting the passage of the reference marker, and a controlling unitcontrolling the formation of the image by the first and second imageforming units, by taking time when the detecting unit detects thepassage of the reference marker as a reference.

According to a mode of the present invention, a method of manufacturingan electronic circuit having a circuitry layer formed on a substratehaving a conductor layer, comprises exposing a photo conductor based onimage information of the circuitry layer to form an electrostatic latentimage on the photo conductor, developing the electrostatic latent imageon the photo conductor by toner containing formation material of thecircuitry layer to form a toner image on the photo conductor,electrostatically transferring the toner image on the photo conductoronto the substrate so that at least a part of the conductor layer iscovered, while removing excessive charges caused in the conductor layeraccompanying the start of the transfer of the toner image, and fixingthe toner image transferred onto the substrate.

According to another mode of the present invention, a method ofmanufacturing an electronic circuit having a circuitry layer formed on asubstrate having a conductor layer, comprises exposing a photo conductorbased on image information of the circuitry layer to form anelectrostatic latent image on the photo conductor, developing theelectrostatic latent image on the photo conductor by toner containingformation material of the circuitry layer to form a toner image on thephoto conductor, electrostatically transferring the toner image on thephoto conductor onto the substrate so that at least a part of theconductor layer is covered, while adding charges of which polarity isreverse to that of the toner to the conductor layer, and fixing thetoner image transferred onto the substrate.

According to still another mode of the present invention, a method ofmanufacturing an electronic circuit having a circuitry layer formed on asubstrate having a conductor layer, comprises exposing a photo conductorbased on image information of the circuitry layer to form anelectrostatic latent image on the photo conductor, developing theelectrostatic latent image on the photo conductor by toner containingformation material of the circuitry layer to form a toner image on thephoto conductor, electrostatically transferring the toner image on thephoto conductor onto the substrate having a conductor buffer layerconnected to the conductor layer so that at least a part of theconductor layer is covered, and fixing the toner image transferred ontothe substrate.

According to yet another mode of the present invention, a method ofmanufacturing an electronic circuit on a substrate using metalparticle-containing toner, comprises charging a photo conductor,exposing the photo conductor which is charged based on image informationto form an electrostatic latent image on the photo conductor, developingthe electrostatic latent image on the photo conductor by the toner toform a toner image on the photo conductor, while controlling an absolutevalue of white contrast of the photo conductor to 200 V or lower,transferring the toner image on the photo conductor onto the substrate,fixing the toner image transferred onto the substrate, and subjectingthe fixed toner image to electroless plating using the metal particlesexposing on a surface of the toner image as nuclei.

According to still another mode of the present invention, a method ofmanufacturing an electronic circuit on a substrate, comprises carryingthe substrate, which is mounted on a predetermined position of a carrierunit using a positioning member, by the carrier unit, detecting thepassage of a reference marker which is provided to the carrier unit andmoves with the substrate, starting exposure a photo conductor based onimage information to form an electrostatic latent image on the photoconductor, by taking time when the passage of the reference marker isdetected as a reference, developing the electrostatic latent image onthe photo conductor by toner to form a toner image on the photoconductor, transferring the toner image on the photo conductor onto thesubstrate carried by the carrier unit, and fixing the toner imagetransferred onto the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Although the present invention will be described with reference to thedrawings, these drawings are presented only for illustrative purposesonly and are by no means intended to limit the invention.

FIG. 1 is a front view showing the schematic structure of an imageforming apparatus according to a first embodiment of the presentinvention.

FIG. 2 is a plan view showing the essential structure of the imageforming apparatus shown in FIG. 1.

FIG. 3 is a view for explaining the state of potential in a conductorlayer according to the conventional method.

FIG. 4 is a sectional view showing a structural example of a wiringboard manufactured by using the image forming apparatus shown in FIG. 1.

FIG. 5 is a view for explaining the state of potential in the conductorlayer when forming an insulating layer by using the image formingapparatus shown in FIG. 1.

FIG. 6 is a plan view showing the essential structure of a modificationexample of the image forming apparatus shown in FIG. 1.

FIG. 7 is a front view showing the schematic structure of an imageforming apparatus according to a second embodiment of the presentinvention.

FIG. 8 is a plan view showing the essential structure of a modificationexample of the image forming apparatus shown in FIG. 7.

FIG. 9 is a plan view schematically showing only the essential structureof an image forming apparatus according to a third embodiment of thepresent invention.

FIG. 10 is a view for explaining the state of potential in a conductorlayer and a conductor buffer layer when forming an insulating layer byusing the image forming apparatus shown in FIG. 9.

FIG. 11 is a plan view showing the schematic structure of an imageforming apparatus according to a fourth embodiment of the presentinvention.

FIG. 12 is a block diagram showing the structure of a control system ofthe image forming apparatus shown in FIG. 11.

FIG. 13 is a flow chart showing an example of formation process of animage using the image forming apparatus shown in FIG. 11.

FIG. 14 is a sectional view showing a structural example of toner usedin the image forming apparatus shown in FIG. 11.

FIG. 15 is a view showing the relationship between white contrast andfog quantity.

FIG. 16 is a front view showing the schematic structure of an imageforming apparatus according to a fifth embodiment of the presentinvention.

FIG. 17 is a block diagram showing the structure of a control system ofthe image forming apparatus shown in FIG. 16.

FIG. 18 is a flowchart showing an example of formation process of animage using the image forming apparatus shown in FIG. 16.

FIG. 19 is a sectional view showing a structural example of a wiringboard having a wiring layer of a single layer, which is manufacturedusing the image forming apparatus shown in FIG. 16.

FIG. 20 is a sectional view showing a structural example of a multilayerwiring board having a plurality of wiring layers, which is manufacturedusing the image forming apparatus shown in FIG. 16.

FIG. 21 is a front view showing the schematic structure of an imageforming apparatus of tandem structure according to a sixth embodiment ofthe present invention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be explained withreference to the drawings. Although the embodiments of the presentinvention will be described based on the drawings, these drawings arepresented only for illustrative purposes only and are by no meansintended to limit the invention.

FIG. 1 and FIG. 2 are views showing the structure of an image formingapparatus according to a first embodiment of the present invention. FIG.1 is a front view schematically showing the structure of the imageforming apparatus, and FIG. 2 is a plan view showing the essentialstructure of the image forming apparatus. An image forming apparatus 10shown in these drawings, to which an electrophotographic system isapplied, is used as a manufacturing apparatus of an electronic circuit,for example. The manufacturing apparatus of the electronic circuit isused for manufacturing an electronic circuit which has, for example, aninsulating layer or a semiconductor layer as a circuitry layer 13 formedon a substrate 12 having a conductor layer 11.

The image forming apparatus 10 is mainly constituted of a photoconductive drum 101 having a photo conductive function, an electrifier102, an exposure unit 104 having a laser generation/scan device 103, adeveloping unit 107 which has a developing machine 106 accommodatingtoner 105 made of forming material of the circuitry layer 13, anelectrostatic transferring unit 109 having a charge supplying mechanism108 for electrostatic transfer, a charge removing unit 111 having anexcessive charge removing mechanism 110 for reducing a potentialdifference in the conductor layer 11 when electrostatically transferringthe toner 105, and a fixing unit 113 having a fixing device 112.

The photo conductive drum 101 is rotatable in the direction of an arrowA in the drawing so as to pass through the electrifier 102, exposureunit 104, developing unit 107 and electrostatic transferring unit 109 inorder. The electrifier 102 charges the photo conductive drum 101 so thatthe surface thereof has a certain potential (negative charges, forexample). Charging methods include, for example, a scorotron chargingmethod, roller charging method, brush charging method, and the like. Theexposure unit 104 irradiates the surface of the photo conductive drum101, on which the negative charges are generated, for example, with alaser beam 114 according to image information (formation pattern) of thecircuitry layer 13, and removes the negative charges on a portionirradiated with the laser beam 114 by a photoelectric effect of a photoconductor, to form an electrostatic latent image (image of charges) 115.

The developing unit 107 supplies the toner (toner) 105 from thedeveloping machine 106 and brings the toner 105 into adhesion with theelectrostatic latent image 115 to form a visible image (toner image)116. The toner image 116 has the shape corresponding to the formationpattern of the circuitry layer 13. The electrostatic transferring unit109 has the charge supplying mechanism 108 supplying charges whosepolarity (positive charges, for example) is reverse to that of the toner105 on the opposite face (back face) side to the formation face of theconductor layer 11 of the substrate 12. In the electrostatictransferring unit 109, the substrate 12 is moved in the same direction(the direction of an arrow B) as the photo conductive drum 101.Electrostatic force between the positive charges added to the back faceside of the substrate 12 and the negative charges of the toner 105causes the toner image 116 to be transferred onto the substrate 12. Inthe drawing, 117 denotes a mechanism subjecting the substrate 12 tocharge removing processing, after the toner image 116 is transferredthereto.

When the transfer of the toner image 116 is started in the electrostatictransferring unit 109, excessive charges are generated near the surfaceof the conductor layer 11, and a potential difference is caused based onthe excessive charges. This potential difference in the conductor layer11 causes transfer failure of the toner image 116. Namely, when a partof the conductor layer 11 is disposed inside an electric field as shownin FIG. 3, the potential difference is caused between the portion of theconductor layer 11 in the electric field and the portion out of theelectric field. Based on the potential difference caused in theconductor layer 11, the toner 105 near the conductor layer 11 isrejected. Thus, the transfer of the toner image 116 may becomedefective.

Therefore, the image forming apparatus 10 of this embodiment has thecharge removing unit 111 which removes the excessive charges in theconductor layer 11 so as to reduce the potential difference caused inthe conductor layer 11 accompanying the start of the transfer of thetoner image 116. The charge removing unit 111 has the excessive chargeremoving mechanism 110 which is so arranged that it is in electricalcontact with a part or an entire face of an exposed face (face where thetoner image 116 is not yet transferred) of the conductor layer 11 towhich the toner image 116 is started to be transferred. In other words,the charge removing unit 111 has the excessive charge removing mechanism110 which is in electrical contact with the exposed face of theconductor layer 11 arranged on the rear side in the moving direction ofthe substrate 12, to which the addition of the positive charges isstarted in the electrostatic transferring unit 109.

The excessive charge removing mechanism 110 has a contact portion 118made of, for example, conductive material. The conductive contactportion 118 is grounded. The conductive contact portion 118 isconstituted of a brush made of, for example, the conductive material sothat it can obtain an excellent contact state with the surface of theconductor layer 11 which moves in the direction of the arrow B in thedrawing. Instead of the conductive brush, the conductive contact portion118 may be constituted of a conductive roller, band-shaped orplate-shaped conductive rubber, and so on. It is preferable that theconductive contact portion 118 has the shape and material which do notcause damage to the surface of the conductor layer 11. Further, it ispreferable that the conductive contact portion 118 has the shape that itis in contact with the entire surface of the conductor layer 11.

The toner image 116 which is transferred onto the substrate 12 in theelectrostatic transferring unit 109 is subjected to heating processingaccording to thermal properties of the toner 105 or ultra violetirradiating processing in the fixing device 112. By performing suchfixing processing, the circuitry layer 13 is formed on the substrate 12.The circuitry layer 13 is formed so as to cover at least a part of theconductor layer 11. After the toner image 116 is transferred, theresidual toner 105 on the surface of the photo conductive drum 101 isremoved and recovered by a not-shown cleaning device.

Next, formation process of the circuitry layer 13 using theabove-described image forming apparatus 10 will be explained. Here, theformation process of the circuitry layer will be described by taking thecase where an insulating layer is formed as the circuitry layer 13 onthe substrate 12 having the conductor layer 11 as an example. FIG. 4 isa sectional view schematically showing a structural example of a wiringboard to which the formation process of the insulating layer 13 of thisembodiment is applied. A wiring board 14 shown in FIG. 4 has a circuitpattern of a single layer structure. Incidentally, the wiring board towhich the formation process of the insulating layer 13 is applied mayhave a multiplayer structure. Moreover, it can be applied to theformation process of the insulating layer 13 of an electronic device,electronic component and the like, besides the wiring board.

The wiring board 14 shown in FIG. 4 has a substrate 12 on which a metalconductor layer 11 is formed. The metal conductor layer 11 has a platingbase layer 15 selectively formed on the substrate 12, and a metalplating layer 16 formed on the surface of the plating base layer 15. Theplating base layer 15 is formed by the electrophotographic system using,for example, insulating resin particles containing metal fine particlesas the toner. By immersing the substrate 12 having the plating baselayer 15 in an electroless plating tank such as Cu, the metal such as Cuprecipitates selectively by using the metal fine particles projectingfrom the surface of the plating base layer 15 as nuclei, whereby themetal plating layer 16 is formed.

At least a part of the surface of the metal conductor layer 11 and thesubstrate 12 is covered with the insulating layer 13. The insulatinglayer 13 is formed to have a desired pattern using theelectrophotographic system. Although its formation pattern is notparticularly limited, the insulating layer 13 is formed so as to coverat least apart of the metal conductor layer 11. Thermosetting resinwhich is generally used as forming material of the insulating layer ofthe wiring board is employed as the material constituting the insulatinglayer 13. The thermosetting resin includes epoxy resin, phenol resin,silicone resin, polyimide resin, bismaleimide resin, cyanate esterresin, bismaleimide-triazine resin, benzocyclobutene resin,polybenzoxazole resin, butadiene resin, polycarbodiimide resin,polyurethane resin, and the like.

The insulating layer 13 is formed using the image forming apparatus 10as follows. First, the insulating resin particles (thermosetting resinparticles, for example) are filled in the developing machine 16 as thetoner 105, and the substrate 12 having the metal conductor layer 11 isset in the image forming apparatus 10. While the photo conductive drum101 is rotated in the direction of the arrow, the substrate 12 is movedin the same direction as the rotating direction of the photo conductivedrum 101. The photo conductive drum 101 is made to pass through theelectrifier 102 and the exposure unit 104 in order, whereby theelectrostatic latent image 115 is formed on its surface corresponding tothe formation pattern of the insulating layer 13. Subsequently, thedeveloping machine 106 supplies the insulating resin particles as thetoner 105 and brings the toner 105 into adhesion with the electrostaticlatent image 115 to form the toner image (insulating resin particleimage) 116.

Next, the toner image 116 is electrostatically transferred onto thesubstrate 12 in the electrostatic transferring unit 109. When theelectrostatic transfer of the toner image 116 is started, the excessivecharges are generated in the metal conductor layer 11. As to suchexcessive charges, the excessive charge removing mechanism 110 beinggrounded is in contact with the exposed face of the metal conductorlayer 11 where the toner image 116 is not yet transferred. Therefore,the excessive charges caused in the metal conductor layer 11 are removedas shown in FIG. 5, and the potential difference can be reduced.Accordingly, it is possible to prevent the phenomenon that the toner(insulating resin particles) 105 on the photo conductive drum 101 isrejected due to the potential difference in the metal conductor layer11.

As described above, the excessive charge removing mechanism 110 is madein contact with the exposed face of the metal conductor layer 11 locatedon the rear side in the moving direction of the substrate 12, to whichthe addition of the positive charges is started in the electrostatictransferring unit 109, so that the potential difference in the metalconductor layer 11 is reduced. Thereby, it is possible to transfer thetoner image 116 to the entire surface of the metal conductor layer 11(especially on the rear end side relative to the moving direction of thesubstrate 12) favorably and securely. By thermally fixing such a tonerimage 116 in the fixing unit 112, for example, the entire surface of themetal conductor layer 11 can be covered by the sound insulating layer13. Namely, the insulating layer 13 can be favorably and securely formedto have the desired pattern on the metal conductor layer 11. Thiscontributes significantly to the improvement of a manufacturing yieldand manufacturing efficiency of the electronic circuit by theelectrophotographic system (wiring board in this embodiment).

Incidentally, the case where the conductive contact portion 118 of theexcessive charge removing mechanism 110 is made in contact with thesurface of the conductor layer 11 directly is explained according to theimage forming apparatus 10 of the above-described embodiment. However,the structure of the excessive charge removing mechanism 110 is notlimited to the above. For example, as shown in FIG. 6, dummy patterns 18which are connected to the conductor layer 11 via leading wires 17 areformed on the substrate 12 in advance. The conductive contact portion118 of the excessive charge removing mechanism 110 may be made incontact with such dummy patterns 18. The substrate 12 shown in FIG. 6has the dummy patterns 18 which are respectively formed on both sides ofthe conductor layer 11 continuously along the moving direction of thesubstrate 12, and the conductive contact portions 118 are in contactwith these dummy patterns 18, respectively.

Even when the excessive charge removing mechanism 110 is thus connectedto the conductor layer 11 via the dummy patterns 18, it is possible toremove the excessive charges caused in the metal conductor layer 11accompanying the start of the electrostatic transfer. Namely, thepotential difference in the conductor layer 11 can be reduced, andtherefore the insulating layer 13 can be formed to have the desiredpattern on the conductor layer 11 favorably and securely. Further, theuse of the dummy patterns 18 eliminates the need to contact theconductive contact portion 118 of the excessive charge removingmechanism 110 with the conductor layer 11 directly, so that theoccurrence of failure due to loss, peeling and the like of the conductorlayer 11 can be prevented.

Next, an image forming apparatus according to a second embodiment of thepresent invention will be explained with reference to FIG. 7. Similarlyto the first embodiment, an image forming apparatus 20 shown in FIG. 7,to which an electrophotographic system is applied, is used as amanufacturing apparatus of an electronic circuit, for example. Themanufacturing apparatus of the electronic circuit is used formanufacturing an electronic circuit which has, for example, aninsulating layer or a semiconductor layer as a circuitry layer 13 formedon a substrate 12 having a conductor layer 11.

Similarly to the image forming apparatus 10 according to the firstembodiment, the image forming apparatus 20 of the second embodiment isconstituted of a photo conductive drum 101, an electrifier 102, anexposure unit 104 having a laser generation/scan device 103, adeveloping unit 107 which has a developing machine 106 accommodatingtoner 105 made of forming material of the circuitry layer 13, anelectrostatic transferring unit 109 having a charge supplying mechanism108, and a fixing unit 113 having a fixing device 112. It should benoted that the respective components 101, 102, 104, 107, 109 and 113 arethe same as those of the image forming apparatus 10 according to thefirst embodiment, and concrete structures thereof are the same as above.

The image forming apparatus 20 has a bias voltage applying unit 120adding charges (positive charges, for example) whose polarity is reverseto that of the toner 105 to the surface of the conductor layer 11,instead of the charge removing unit 111 according to the firstembodiment. The bias voltage applying unit 120 has a bias chargesupplying mechanism 122 which is connected to a power supply 121, forexample, and the bias charge supplying mechanism 122 is provided with acontact portion 123 made of conductive material. The conductive contactportion 123 is constituted of a brush made of, for example, theconductive material so that it can obtain an excellent contact statewith the surface of the conductor layer 11 which moves in the directionof an arrow B in the drawing. Instead of the conductive brush, theconductive contact portion 123 may be constituted of a conductiveroller, band-shaped or plate-shaped conductive rubber, and so on. It ispreferable that the conductive contact portion 123 has the shape to bein contact with the entire surface or a part of the surface of theconductor layer 11.

When the transfer of a toner image 116 is started in the electrostatictransferring unit 109, excessive charges are generated in the conductorlayer 11 as described above, and a potential difference is caused basedon the excessive charges. This potential difference in the conductorlayer 11 causes transfer failure of the toner image 116. Hence, the biasvoltage applying unit 120 which supplies charges, whose polarity isreverse to the negative charges of the toner 105 and is the same as thepositive charges supplied from the electrostatic transferring unit 109,from the front face side of the conductor layer 11 is provided, so as toactively reduce the potential-difference caused in the conductor layer11 accompanying the start of the transfer of the toner image 116. Thebias voltage applying unit 120 has the bias charge supplying mechanism122 which is arranged to be in electrical contact with an exposed face(face where the toner image 116 is not yet transferred) of the conductorlayer 11 positioned on the rear side in the moving direction of thesubstrate 12, to which the addition of the positive charges is startedin the electrostatic transferring unit 109.

Supposing that a voltage applied to the electrostatic transferring unit109 is, for example, 800 to 2000 V, and a potential of the photoconductive drum 101 is 0 V, it is preferable to apply a voltage ofapproximately 600 to 1200 V (the voltage lower than the electrostatictransferring unit 109) to the bias charge supplying mechanism 122. Whenthe voltage applied to the bias charge supplying mechanism 122 is toolow, there is the possibility that the effect for reducing the potentialdifference in the conductor layer 11 becomes insufficient. Meanwhile,when the voltage applied to the bias charge supplying mechanism 122 istoo high, there is the possibility that the toner 105 is drawn to thesubstrate 12 before reaching the electrostatic transferring unit 109.

Since the positive charges whose polarity is reverse to that of thetoner 105 are thus actively supplied to the front face side of theconductor layer 11, it is possible to facilitate the transfer of thetoner image 116 such as the insulating resin particle image onto theconductor layer 11. Therefore, it is possible to cover the entiresurface of the conductor layer 11 (especially on the rear end siderelative to the moving direction of the substrate 12) by the soundcircuitry layer 13 such as the insulating layer. Namely, the circuitrylayer 13 such as the insulating layer can be formed to have the desiredpattern on the metal conductor layer 11 favorably and securely. Thiscontributes significantly to the improvement of a manufacturing yieldand manufacturing efficiency of the electronic circuit by theelectrophotographic system (wiring board in this embodiment).Incidentally, the concrete formation process of the circuitry layer 13such as the insulating layer is the same as that of the firstembodiment.

In the image forming apparatus 20 of the above-described embodiment, thecase where the bias charge supplying mechanism 122 is made in contactwith the surface of the conductor layer 11 directly is explained.However, the structure of the bias charge supplying mechanism 122 is notlimited to the above. For example, as shown in FIG. 8, dummy patterns 18which are connected to the conductor layer 11 via leading wires 17 areformed on the substrate 12 in advance, and the bias charge supplyingmechanism 122 may be connected to these dummy patterns 18. The substrate12 shown in FIG. 8 has the dummy patterns 18 which are respectivelyformed on both sides of the conductor layer 11 continuously along themoving direction of the substrate 12, respectively, and the conductivecontact portions 123 of the bias charge supplying mechanism 122 are incontact with these dummy patterns 18, respectively.

Even when the bias charge supplying mechanism 122 is thus connected tothe conductor layer 11 via the dummy patterns 18, it is possible toreduce the potential difference in the conductor layer 11 accompanyingthe start of the transfer of the toner image 116. By reducing thepotential difference in the conductor layer 11 by such structure, it isalso possible to favorably and securely form the circuitry layer 13 suchas the insulating layer to have the desired pattern on the conductorlayer 11. Further, the use of the dummy patterns 18 eliminates the needto contact the conductive contact portion 123 of the bias chargesupplying mechanism 122 with the conductor layer 11 directly, so thatthe occurrence of failure due to loss, peeling and the like of theconductor layer 11 can be prevented.

Next, an image forming apparatus according to a third embodiment of thepresent invention will be explained with reference to FIG. 9. Similarlyto the first embodiment, an image forming apparatus 30 shown in FIG. 9,to which an electrophotographic system is applied, is used as amanufacturing apparatus of an electronic circuit, for example. Themanufacturing apparatus of the electronic circuit is used formanufacturing an electronic circuit which has, for example, aninsulating layer or a semiconductor layer as a circuitry layer 13 formedon a substrate 12 having a conductor layer 11.

It should be noted that FIG. 9 shows only the essential structure of theimage forming apparatus 30 according to the third embodiment, and itsmain part is the same as that of the image forming apparatus 10according to the first embodiment. That is, the image forming apparatus30 is constituted of a photo conductive drum 101, an electrifier, anexposure unit having a laser generation/scan device, a developing unitwhich has a developing machine accommodating toner (toner) made offorming material of the circuitry layer, an electrostatic transferringunit having a charge supplying mechanism 108, and a fixing unit having afixing device, similarly to the image forming apparatus 10 according tothe first embodiment. The respective components are the same as those ofthe image forming apparatus 10 according to the first embodiment, andconcrete structures thereof are the same as above.

In the image forming apparatus 30 according to the third embodiment, thesubstrate 12 which has a conductive buffer layer 31 connected to therear side in the moving direction of the conductor layer 11 (the rearside in the moving direction of the substrate 12 shown by an arrow B) isused. That is, the conductive buffer layer 31 which is connected to therear side in the moving direction of the conductor layer 11 is formed onthe surface of the substrate 12 in advance, so that the conductivebuffer layer 31 absorbs excessive charges generated in the conductorlayer 11 accompanying the start of transfer of a toner image. Thefunction of the conductive buffer layer 31 is similar to that of thegrounding to the conductor layer 11 according to the first embodiment.

Formation process of the insulating layer 13 using the image formingapparatus 30 is performed as follows. First, similarly to the firstembodiment, the photo conductive drum 101 is made to pass through theelectrifier and the exposure unit in order, whereby an electrostaticlatent image is formed on its surface corresponding to a formationpattern of the insulating layer 13. Next, the developing machinesupplies insulating resin particles as the toner 105 and brings thetoner 105 into adhesion with the electrostatic latent image to form thetoner image (insulating resin particle image). Subsequently, the tonerimage is electrostatically transferred onto the substrate 12 in theelectrostatic transferring unit.

When the electrostatic transfer of the toner 105 onto the substrate 12is started as shown in FIG. 10, the excessive charges aregenerated inthe conductor layer 11. As to such excessive charges, the buffer layer31 is connected to the rear side in the moving direction of theconductor layer 11, and hence it is possible to reduce a potentialdifference due to the excessive charges in the conductive buffer layer31. Namely, the potential difference caused in the conductor layer 11 bythe generated excessive charges has an inclination based on the totallength and the like of the conductor layer 11 and the conductive bufferlayer 31, whereby the potential difference can be reduced. Thus, it ispossible to prevent the occurrence of the phenomenon that the toner 105on the photo conductive drum 101 is rejected due to the potentialdifference in the conductor layer 11.

Incidentally, the length of the conductive buffer layer 31 (the lengthrelative to the moving direction of the substrate 12) is set so that itcan absorb the excessive charges in the conductor layer 11 and reducethe potential difference. While the length of the conductive bufferlayer 31 which can obtain such an effect varies with the area, thicknessand the like of the conductor layer 11 and the conductive buffer layer31, it is preferable to set the length of the conductive buffer layer 31so that the total length L₂ of the conductor layer 11 and the conductivebuffer layer 31 is approximately two or more times as long as the lengthL₁ of the conductor layer 11 (2L₁≦L₂). When the length of the conductivebuffer layer 31 is too short, there is the possibility that theinclination of the potential difference due to the excessive charges isnot reduced sufficiently.

As described above, since the potential difference in the conductorlayer 11 can be reduced by connecting the conductive buffer layer 31 tothe rear side in the moving direction of the conductor layer 11 inadvance, it is possible to transfer the toner 105 such as the insulatingresin particles to the entire surface of the conductor layer 11(especially on the rear end side relative to the moving direction of thesubstrate 12) favorably and securely. Namely, the circuitry layer 13such as the insulating layer can be formed to have the desired patternon the conductor layer 11 favorably and securely. This contributessignificantly to the improvement of a manufacturing yield andmanufacturing efficiency of the electronic circuit by theelectrophotographic system (electronic circuit constituting theessential part such as the wiring board, semiconductor element and thelike).

In the above-described embodiments, the case where the insulating layeris formed as the circuitry layer 13 is mainly explained. However, thecircuitry layer 13 is not limited to the insulating layer. For example,when the electrophotographic system is applied to the formation of asemiconductor layer, transfer failure may be caused similarly to theinsulating layer, depending on the magnitude of an electric field to beapplied. The above-described image forming apparatus according to eachembodiment is effective for the formation of such a semiconductor layer.When the semiconductor layer is formed using the image formingapparatus, an organic semiconductor, as well as an inorganicsemiconductor such as Si, may be used.

Next, an image forming apparatus according to a fourth embodiment of thepresent invention will be explained with reference to FIG. 11. FIG. 11is a front view showing the schematic structure of an image formingapparatus 40 according to the fourth embodiment of the presentinvention. Similarly to the above-described embodiments, the imageforming apparatus 40 shown in FIG. 11, to which an electrophotographicsystem is applied, is used as a manufacturing apparatus of an electroniccircuit, for example. The manufacturing apparatus of the electroniccircuit is used for forming a plating base layer of a conductor layer ofa wiring board, and the like.

The image forming apparatus 40 shown in FIG. 11 is mainly constituted ofa photo conductor 401, a charging device 402, an aligner 403, adeveloping device 404, a cleaning blade 405, a sheet metal 406, atransferring device 407, a charge removing device 408, and a recoverysheet 409. The aligner 403 exposes the photo conductor 401 based onpattern information (image information) created by CAD, for example. Thecleaning blade 405 is made of urethane rubber, for example, and issupported by the sheet metal 406. The sheet metal 406 is abutted againstthe photo conductor 401 with a specified load by a not-shown spring. Therecovery sheet 409 receives toner dropping down when the cleaning blade405 scrapes the residual toner on the surface of the photo conductor401.

FIG. 12 shows the structure of a control system of the image formingapparatus 40. The control system of the image forming apparatus 40 ismainly constituted of a CPU 410 for governing entire control, a ROM 411for storing programs and the like, a RAM 412 for temporarily storingdata, an exposure controlling unit 413 for controlling the aligner 403,a developing and cleaning controlling unit 414 for controlling thedeveloping device 404, a process controlling unit 415 for controllingeach process of charging, exposing, developing and transferring, acarrier controlling unit 416 for controlling a not-shown carrier, and ahigh voltage controlling unit 417 for controlling the state ofapplication of high voltages such as a grid voltage of the chargingdevice 402, a developing bias of the developing device 404 and the like.

Next, the operation of forming the image of the pattern information on asubstrate P by using the image forming apparatus 40 according to thefourth embodiment will be explained with reference to a flowchart shownin FIG. 13. The following operation is controlled by the CPU 410. First,the photo conductor 401 is rotated in the direction of an arrow A in thedrawing (ST1). Then, the photo conductor 401 is charged negative by thecharging device 402 uniformly (ST2). Subsequently, the photo conductor401 is exposed by the aligner 403 (ST3), and an electrostatic latentimage based on the pattern information is formed on its surface. By thedeveloping device 404, the electrostatic latent image on the photoconductor 1 is reversely developed by negative-charged toner to be atoner image (ST4).

The toner forming the toner image is made of binder containing metalparticles. Thermoplastic resin is generally used as normal toner forelectrophotography. However, according to the toner for forming theelectronic circuit, the circuit pattern is required to be stable inheating in the subsequent step, and therefore thermosetting resin isused as the binder. The thermosetting resin for the binder includesphenol resin, melamine resin, furan resin, epoxy resin, unsaturatedpolyester resin, diallylphthalate resin, polyimide resin and the like. Aglass epoxy substrate and a phenol resin substrate (Bakelite(Trademark), for example) are generally used as the material of thesubstrate P. It is preferable to use resin having high affinity to thesesubstrates such as epoxy resin, phenol resin, or the mixture thereof asthe material of the toner. However, it is possible to use thethermoplastic resin in the case of forming a conductor layer of onelayer only.

The toner is formed by mixing and dispersing conductive fine metalpowder whose particle size is equal to or smaller than 1 μm in the abovebinder in the range of 15 to 75 mass %. Transition metal such as Cu, Ni,Co, Ag, Pd, Rh, Au, Pt, Ir and the like is used as the conductive finemetal powder. Some of the metal fine particles dispersed in the binderare exposed partially on the surface of the toner. The circuit patternis formed on the substrate P by the toner, cured by heating, andthereafter subjected to electroless plating, whereby a metal platinglayer which uniformly covers the entire toner pattern can be obtainedusing the exposed metal fine particles as nuclei. The conductor layer isconstituted of the toner layer (plating base layer) and the metalplating layer.

The content of the fine metal powder in the toner is preferably withinthe range of 15 to 75 mass %. When the content ratio of the fine metalpowder becomes too large, electrical resistance of the toner decreasesto reduce the quantity of the charges, whereby fog tends to be caused.Meanwhile, when the content ratio of the fine metal powder becomes toosmall, it is impossible to give enough conductivity to the wiringpattern even after the electroless plating processing. Additionally, itis preferable that the particle size of the fine metal powder is equalto or smaller than 1 μm. When the particle size of the fine metal powderis too large, the dispersion in the binder becomes insufficient, theamount of the exposure of the fine metal powder on the surface of thetoner and the amount of the metal fine particles which are free from thebinder increase, and as a result, the fog is easily caused. Morepreferably, the particle size of the fine metal powder is equal to orsmaller than 0.7 μm.

Besides the binder and the fine metal powder, the toner may contain wax,disperse auxiliary agent, coloring agent, charge controlling agent andthe like as necessary. These raw materials are mixed uniformly andkneaded with heating using a kneading machine such as a pressurekneader, Banbury mixer, two rolls, three rolls, twin-screw extruder, andthe like. At this time, the temperature and time in kneading arecontrolled in order to prevent the binder from curing. The sufficientlykneaded toner is cooled and thereafter ground coarsely. Then, it isfinely ground using a jet grinder and the like, and particle sizedistribution is adjusted using an air classifier and the like. After itis ground and classified, an external addictive such as silica, titaniumoxide and the like may be added further to the surface of the toner asnecessary. Preferably, the particle size of the toner is equal to orsmaller than 12 μm in the 50% particle size on the volume basis, andmore preferably, it is equal to or smaller than 10 μm.

It should be noted that Multisizer II manufactured by Beckman Coulter,Inc. is used for measuring the particle size distribution of the toner.AG-4311LCR meter manufactured by Ando Electric Co., Ltd. issued formeasuring volume resistivity of the toner. A resistive component of thetoner is measured by using a pellet which is molded by the toner withthe pressure of 30 ton and has the thickness of about 1.5 mm as aspecimen, and by adding the alternating current of 1 kHz, 5 V under thecondition of 30° C. The height of the toner on the photo conductor ismeasured by a laser displacement microscope.

Hereinafter, a concrete example of forming the toner used in thisembodiment will be explained. The epoxy resin (50 mass %) as the binderand copper particles whose particle size is 0.7 μM (50 mass %) as themetal fine particles are uniformly mixed by a Henschel mixer for fiveminutes, and thereafter kneaded by the pressure kneader under thetemperature condition of 90° C. for ten minutes. After gelation, it isquenched and ground coarsely by a hammer mill to be equal to or smallerthan 2 mm. Subsequently, it is finely ground and classified to be thesize of 8 μm using a I-type jet grinder and DSX classifier. The particlesize is thus adjusted. The obtained toner and silica R974 (1 mass %) aremixed by the Henschel mixer for ten minutes and thereafter made to passthrough a 200-mesh screen, to thereby obtain the toner for forming thewiring pattern (toner for plating base layer). Volume specificresistivity of the toner is 2.9×10¹⁰ Ωcm.

Similarly, the epoxy resin is kneaded by the pressure kneader under thetemperature condition of 90° C. for ten minutes. After gelation, it isquenched and ground coarsely by the hammer mill to be equal to orsmaller than 2 mm. Subsequently, it is finely ground and classified tobe the size of 10 μm using the I-type jet grinder and DSX classifier.The obtained toner and silica R974 (1 mass %) are mixed by the Henschelmixer for ten minutes and thereafter made to pass through the 200-meshscreen, to thereby obtain the toner for forming the insulating pattern.

FIG. 14 shows the structure of metal particle-containing toner 41. Thistoner particle 41 has copper particles 43 dispersed in binder resin 42.Some of the copper particles 43 are exposed from the surface of thebinder resin 42. This exposure of the copper particles 43 is importantin copper plating. Therefore, it is necessary that the copper particles43 are exposed on the surface of the toner particle 41 to some extent.In this embodiment, a two-component developer in which a ferrite carriercoated with silicone-based resin whose average particle size is 60 μmand the above-described toner are mixed at a predetermined mixing ratiois formed to be used. It is of course possible to apply a one-componentdeveloping system.

The developed toner image on the photo conductor 401 is rotated to atransfer position to a substrate P. The toner image is electrostaticallytransferred to the substrate P by positive charges added to the backface of the substrate P in the transferring device 407 (ST5). At thistime, the substrate P is carried by the not-shown carrier at the speedalmost the same as a circumferential speed of the photo conductor 401.Thereafter, the substrate P is removed with the charges by the chargeremoving device 408, helped to peel off from the photo conductor 401 topeel off from the photo conductor 401 (ST6). The toner remaining on thephoto conductor 401 as transfer remaining toner, out of the toner imagetransferred from the photo conductor 401 to the substrate P, is scrapedby the cleaning blade 405 (ST7). After the residual toner is scraped,the photo conductor 401 is charged again (ST2) and the toner image canbe formed on the photo conductor 401 without interruption.

Incidentally, this embodiment shows the case where the toner image istransferred from the photo conductor 401 to the substrate P by theelectrostatic transfer. However, the transfer of the toner image is notlimited to the above. For example, it is possible to transfer the tonerimage from the photo conductor 401 to an intermediate transfer bodytemporarily, and transfer it from the intermediate transfer body to thesubstrate P. In this case, the transfer remaining toner is similarlygenerated on the photo conductor 401, and hence it can be applied as amodification example of this embodiment. Besides the electrostatictransfer system, other known transfer systems such as adhesive transferand pressure transfer can be employed.

Next, “fog” in this embodiment will be explained. The charging device402 for negative-charging the photo conductor 401 is a scorotroncharging device, for example, and the quantity of the charges to beadded to the photo conductor 401 can be changed by changing the gridvoltage by the high voltage controlling unit 417. Further, thedeveloping bias is applied to a developing roller 404 a of thedeveloping device 404 by the high voltage controlling unit 417. In thisembodiment, the developing bias of DC-500 V is used. It is also possibleto use the developing bias of DC+AC, and in such a case, the value of aDC constituent may be considered as the following developing bias value.

FIG. 15 shows the change when a surface potential V₀ of the photoconductor 401 is changed from −450 V to −800 V, taking the “fog” as theordinate, and white contrast as the abscissa. The white contrast isshown by ΔV_(c)=V₀−V_(d). V₀ designates the surface potential of thephoto conductor at a developing point, and V_(d) designates the DCconstituent of the developing bias applied to the developing roller 404a. The image is formed as follows. The toner image based on the wiringdata (pattern information) having the width of 150 μm and the pitch of300 μm is transferred onto a glass epoxy substrate (substrate P). Afterthat, it is heated on a hot plate at the temperature of 160° C. for tenminutes, whereby the toner is cured by heating (fixing). In order tomeasure the “fog”, it is also transferred to a plain paper and fixedthereon. A difference of light reflectance of the image transferred tothe paper from that of a white paper without being transferred ismeasured as the “fog”.

As a result of this, when the “fog” is equal to or smaller than 2%, itis possible to obtain a satisfactory pattern with less dirt in theperiphery of the image and sticking of the toner to a non-image part.Moreover, the glass epoxy substrate which obtains the wiring pattern bythe above-descried image formation is subjected to electroless copperplating processing using the copper particles exposed from the surfaceof the cured toner as nuclei. Thus, the conductivity of the wiring layerformed on the glass epoxy substrate is secured. No problem is caused ina continuity test and insulation test of the wiring pattern with securedconductivity which are performed after that.

When the white contrast is +50V and −300 V, the “fog” exceeds 2%. Theglass epoxy substrate to which the wiring pattern is formed based on theimage formation with such “fog” is subjected to the electroless copperplating processing to secure the conductivity and then, the continuitytest and insulation test of the wiring pattern with the securedconductivity are performed. As a result of this, insulation performanceis insufficient. Therefore, the favorable white contrast of the photoconductor 401 is within the range from 0 to −200 V. More preferably, thewhite contrast is within the range from −50 V to −150 V.

Further, when the similar tests are performed using toner for formingthe insulating pattern which is formed without adding the copperparticles, the volume specific resistivity of the toner is 7.9×10¹⁰ Ωcm,and the satisfactory pattern with less dirt in the periphery of theimage and sticking of the toner to the non-image part can be obtainedwhen the white contrast is within the range from 0 to −300 V. As aresult of this, the toner containing the copper particles tends to causecharge injection under a strong electric field because volumeresistivity of the toner decreases and some of the copper particles areexposed on the surface of the toner, as compared to the toner withoutcontaining the copper particles. After the charge injection, the tonerhas the positive polarity and adheres to the non-image part of the photoconductor 401 as the “fog”.

When the absolute value of the white contrast of the photo conductor 401is equal to or lower than 200 V, more preferably, equal to or lower than150 V, the level of the above-described charge injection can be keptwithin an allowance level. Thus, it is supposed that the “fog” can bereduced to the level without any practical problems. Accordingly, thetwo-component developing system is superior to the contact one-componentdeveloping system with a large development field, in order to obtain thesatisfactory wiring pattern with the less “fog”.

According to the image forming apparatus 40 of this embodiment describedthus far, the plating base layer of the conductor layer constituting thewiring board on the substrate is formed on the substrate by developingthe electrostatic latent image by the metal particle-containing toner,transferring the toner image and the like, so that it is possible toform the clear circuit pattern with the less “fog”. Whereby, theproblems such as a short circuit of the wiring layer and the like can beprevented, and hence the wiring board with high reliability can bemanufactured with a high yield.

Next, an image forming apparatus according a fifth embodiment of thepresent invention will be explained with reference to FIG. 16. FIG. 16is a front view showing the schematic structure of an image formingapparatus 50 according to the fifth embodiment of the present invention.FIG. 17 is a block diagram showing the structure of a control system ofthe image forming apparatus 50 shown in FIG. 16. Similarly to the fourthembodiment described above, the image forming apparatus 50 of the fifthembodiment shown in these drawings, to which an electrophotographicsystem is applied, is used as a manufacturing apparatus of an electroniccircuit, for example. The manufacturing apparatus of the electroniccircuit is used for forming a plating base layer of a conductor layer ofa wiring board, an insulating layer covering the conductor layer, andthe like. The conductor layer is formed on a substrate for theelectronic circuit as a wiring pattern of one layer or multilayerstructure.

The image forming apparatus 50 according to the fifth embodiment has aCPU 520 for governing entire control, a ROM 521 for storing a controlprogram, a RAM 522 for storing data, and an operation unit 527 forinterfacing with users. The CPU 520 responds to various instructionsinputted by the user via the operation unit 527 to control therespective units in the image forming apparatus 50 comprehensively.Further, the image forming apparatus 50 has a laser driver 523 fordriving a semiconductor laser oscillator (not shown) of an aligner 503according to image data supplied from the exterior, a polygon motordriver 524 for driving a polygon motor (not shown) of the aligner 503, acarrier driving unit 525 for driving a transfer material carrier unit507 to control the carry of a substrate P, a charging device 502, and aprocess controlling unit 526 for controlling each process of charging,developing and transferring by using developing devices 504A, 504B and atransferring device 508, and so on.

FIG. 18 is a flowchart showing an example of basic operation of theimage forming apparatus 50. Hereinafter, the operation of the imageforming apparatus 50 will be explained with reference to FIG. 18. Aphoto conductor 501 is rotated in the direction of an arrow A in thedrawing, and then charged negative by the charging device 502 uniformly(ST1). The substrate P has holes for positioning. By positioning pins509 penetrating the holes of the substrate P, the substrate P is mountedon the transfer material carrier unit 507 while being positioned (ST2).

The substrate P has a rectangular shape, and has the holes at its fourcorners. The transfer material carrier unit 507 has the four positioningpins 509. An interval between the pin 509 in the drawing and the pinpositioned in the back thereof (not shown) is set to be wider than thewidth of the photo conductor 501 in a main-scan direction (longitudinaldirection) when developing, in order to prevent the pins from touchingthe photo conductor 501. Such positioning pins 509 decide the positionof the substrate P on the transfer material carrier unit 507.

In a stage before the photo conductor 501 is rotationally driven, thetransfer material carrier unit 507 is arranged at its initial positionwhich is the right end of the apparatus. After a predetermined time fromthe start of the drive of the photo conductor 501 in response to a printstart signal from the operation unit 527, the transfer material carrierunit 507 is accelerated in the direction of an arrow B by the carrierdriving unit 525 to move at a constant speed (ST3).

The transfer material carrier unit 507 is provided with a referencemarker 510. The passage of the reference marker 510 is detected by areference marker detecting unit 511 provided on the apparatus main bodyside (YES in ST4). The CPU 520 takes the time when the passage of thereference marker 510 is detected as a reference to start the exposure bythe aligner 503 (ST5). The aligner 503 exposes and scans the photoconductor 501 to and with a laser beam based on image data, and forms anelectrostatic latent image corresponding to a circuit pattern (wiringpattern and insulating layer pattern) on the surface of the photoconductor 501. The image data is data created by CAD, for example.

The reference marker 510 may be disposed on top of the transfer materialcarrier unit 507. In this case, the reference marker detecting unit 511is disposed so as to detect the reference marker 510 disposed on top ofthe transfer material carrier unit 507. Moreover, the reference marker510 may be provided on the substrate P disposed on the transfer materialcarrier unit 507. The reference marker detecting unit 511 is not limitedto detect the reference marker provided on the substrate P, but it maydetect an image formed on the surface of the substrate P as a referencemarker.

Each of the developing devices 504A and 504B reversely develops theelectrostatic latent image on the photo conductor 501 by toner chargedto a negative potential, to form a toner image (ST6). The developingdevices 504A and 504B form the toner images corresponding to the circuitpatterns which are different from each other on the photo conductor 501,as will be described later. The toner image on the photo conductor 501rotates to a transfer position to the substrate P. The toner image iselectrostatically transferred by the transferring device 508 onto thesubstrate P by a positive bias voltage added to the back face of thesubstrate P (lower side in the drawing) (ST7).

The substrate P which is mounted on the transfer material carrier unit507 moves at the same speed as a circumferential speed of the photoconductor 501. The toner remaining on the photo conductor 501 astransfer remaining toner, out of the toner image transferred from thephoto conductor 501 to the substrate P, is scraped by a cleaning blade505. The cleaning blade 505 is made of urethane rubber, for example, andis supported by a sheet metal 506. The sheet metal 506 is abuttedagainst the photo conductor 501 with a specified load by a not-shownspring. After the residual toner is scraped, the photo conductor 501 ischarged again by the charging device 502 and the toner image can beformed on the photo conductor 501 without interruption.

Although the pin 9 is used for positioning the substrate P on thetransfer material carrier unit 507 according to this embodiment, otherpositioning means such as a grip for mating corners can be used.Further, although the reference marker 510 is equipped to the transfermaterial carrier unit 507, similar accuracy of position can be obtainedeven when a mark is printed on the substrate P.

The substrate P, onto which the transfer is completed, moves to the leftend of the apparatus together with the transfer material carrier unit507, decelerates and stops. Further, the photo conductor 501 also stops(ST8). Then, the substrate P is manually removed from the transfermaterial carrier unit 507. After that, it is heated on a hot plate atthe temperature of 160° C. for ten minutes, for example, whereby thetoner is cured by heating (fixing) (ST9). Besides the electrostatictransfer, other known transfer methods such as adhesive transfer andpressure transfer may be employed in transferring the toner image. It ispossible to transfer the toner image to an intermediate transfer bodytemporarily, and transfer it from the intermediate transfer body ontothe substrate.

The image forming apparatus 50 according to this embodiment has thedeveloping device 504A for developing the electrostatic latent image onthe photo conductor 501 by the metal particle-containing toner and thedeveloping device 504B for developing the electrostatic latent image onthe photo conductor 501 by the toner for forming the insulating pattern.Abutment and alienation of the developing devices 504A and 504B againstand from the photo conductor 501 are possible depending on the patternto be printed. In the case of forming the wiring pattern (to become theconductor layer by plating), the developing device 504A is abuttedagainst the photo conductor 501. In the case of forming the insulatingpattern, the developing device 504B is abutted against the photoconductor 501.

FIG. 19 is a sectional view showing the essential structure of a wiringboard 60 having a wiring layer of a single layer, which is manufacturedusing the image forming apparatus 50 shown in FIG. 16. The wiring board60 has a substrate 61 (P), a non-conductive metal-containing resin layer62 selectively formed on the substrate 61, a conductor metal layer 63formed on the metal-containing resin layer 62, and a resin layer(insulating layer) 64 selectively formed on the substrate 61. Thefollowing is the explanation of an example of formation process of thewiring board 60.

First, a visible image (wiring pattern) of metal-containing resinparticles is formed on the photo conductor 501 using the developingdevice 504A, and the visible image (toner image) is electrostaticallytransferred onto the substrate P by the transferring device 508. Next,the metal-containing resin particles transferred onto the substrate Pare thermally melted and cured thereafter to form the metal-containingresin layer 62 integrated with the metal-containing resin particles.Since the metal-containing resin layer 62 does not have a conductiveproperty, it is subjected to electroless plating processing to form theconductor metal layer 63. The conductor metal layer 63 is formed bymaking the metal such as Cu precipitate selectively using the metalparticles exposing on the surface of the metal-containing resin layer 62as nuclei. Thus, it is possible to form the wiring pattern havingexcellent conductivity.

Next, a visible image (insulating pattern) of resin particles is formedon the photo conductor 501 using the developing device 504B, and thevisible image (toner image) is electrostatically transferred onto thesubstrate P by the transferring device 508. Then, the transferred resinparticles are thermally melted and cured thereafter to form the resinlayer 64 integrated with the resin particles. Thus, it is possible toform the excellent insulating pattern on the substrate P. Here, sincethe image forming apparatus 50 has the positioning means and theposition detecting means of the substrate P, it is possible to enhanceaccuracy of positioning of the conductor metal layer 63 and the resinlayer 64, that is, accuracy of form of the electronic circuit.

By performing the above-described formation process of the wiringpattern and the formation process of the insulating pattern by turns, itis possible to manufacture a multilayer wiring board having a pluralityof wiring layers. FIG. 20 shows the essential structure of a multilayerwiring board 70 thus manufactured. The multilayer wiring board 70 shownin FIG. 20 has a substrate 71 (P), a non-conductive metal-containingresin layer 72 formed on the substrate 71 selectively, a wiring pattern73 formed on the metal-containing resin layer 72, an insulating pattern74 formed on the substrate 71 and the wiring pattern 73 selectively, anda via 75 filled in a recessed portion formed by the wiring pattern 73and the insulating pattern 74.

Further, the multilayer wiring board 70 has a metal-containing resinlayer 76 formed on the insulating pattern 74 and the via 75 selectively,a wiring pattern 77 formed on the metal-containing resin layer 76 andthe via 75, an insulating pattern 78 formed on the insulating pattern 74and the wiring pattern 77 selectively, and a via 79 filled in a recessedportion formed by the wiring pattern 77 and the insulating pattern 78.The wiring patterns 74 and 78 are made of insulating resin.Incidentally, it is possible to layer the respective structure describedabove further to form a third layer, fourth layer and so on.

This embodiment shows the structure in which the two-tired developingdevices 504A and 504B are arranged along the circumferential directionof the photo conductor 501. However, the number and arrangement of thedeveloping devices 504A and 504B are not limited to the above. There isno problem in the structure of mounting only one developing device withrespect to the photo conductor, and replacing the developing devicesmanually or automatically depending on the toner to be printed. Amodification example of this embodiment includes an image formingapparatus having the so-called tandem structure in which another photoconductor and developing device are arranged on a downstream side in themoving direction B of the transfer material carrier unit 507.

FIG. 21 is a front view showing the structure of an image formingapparatus 80 to which the tandem structure is applied as a sixthembodiment of the present invention. Incidentally, the same numerals andsymbols are given to designate the same components as theabove-described fifth embodiment, and explanations thereof are partlyomitted. The image forming apparatus 80 has a first image forming unit81 and a second image forming unit 82.

The first image forming unit 81 has a first photo conductor 501A, afirst charging device 502A, a first aligner 503A, a first developingdevice 504A for developing an electrostatic latent image on the firstphoto conductor 501A by metal particle-containing toner, a firsttransferring device 508A for transferring a toner image on the firstphotoconductor 501A onto a substrate P, and further a detecting unit511. The second image forming unit 82 has a second photo conductor 501B,a second charging device 502B, a second aligner 503B, a seconddeveloping device 504B for developing an electrostatic latent image onthe second photo conductor 501B by toner for forming an insulatingpattern, and a second transferring device 508B for transferring a tonerimage on the second photo conductor 501B onto the substrate P.

After the metal particle-containing toner is transferred onto thesubstrate P by the first image forming unit 81, a carrier driving unit525 carries the substrate P so as to move between the second photoconductor 501B and the second transferring device 508B, under thecontrol of a CPU 520. At this time, an image is not formed in the secondimage forming unit 82. Metal-containing resin particles transferred ontothe substrate P are thermally melted and cured thereafter to form ametal-containing resin layer integrated with the metal-containing resinparticles. Since the metal-containing resin layer does not have aconductive property, the metal-containing resin layer is subjected toelectroless plating processing of Cu so that Cu is made precipitateselectively by using metal particles exposing on the surface of themetal-containing resin layer as nuclei. Thus, it is possible to obtainthe wiring pattern having excellent conductivity.

Next, the substrate P is mounted on a transfer material carrier unit 507in order to form an insulating pattern. The insulating pattern istransferred in an overlapping manner onto the wiring pattern on thesubstrate P by the second image forming unit 82. At this time, an imageis not formed in the first image forming unit 81. The CPU 520 takes timewhen the passage of a reference marker 510 is detected by a detectingunit 511 as a reference to allow the second aligner 503B to start theexposure of the second photo conductor 510B. Thereafter, the insulatingpattern consisting of the resin particles is formed on the second photoconductor 501B by the second developing device 504B. Subsequently, thetoner image of the insulating pattern is electrostatically transferredonto the substrate P by the second transferring device 508B, and isheated as above. Thus, the circuit pattern shown in FIG. 19 is formed.

According to this embodiment described thus far, the substrate P ispositioned and mounted on the transfer material carrier unit 507, andthe exposure to the photo conductors 501A and 501B is started by takingthe time when the passage of the reference marker 510 of the transfermaterial carrier unit 507 is detected as the reference. Accordingly, thewiring layer and the insulating layer can be formed with high accuracyof position. This also applies to the case where the wiring layers andthe insulating layers are formed in multiple layers. When the wiringpattern and the insulating pattern are actually formed using the imageforming apparatuses shown in FIG. 16 and FIG. 21, a deviation of thepatterns can be kept within 200 μm at a maximum, in both of main-scandirection and sub-scan direction of the aligner 503. Further, bydevising the shape of the insulating pattern and the shape of aconnecting portion (via) between the wiring layers, it is possible toobtain the wiring board without any practical problems.

It should be noted that the present invention is not limited to theabove-described embodiments, and any modification can be made at thestage of execution without departing from a technical scope of thepresent invention. Further, all possible combinations of the respectiveembodiments can be made as necessary to obtain combined effects.Moreover, the above-described embodiments include inventions at variousstages, and various inventions may be extracted by properly combining aplurality of components-disclosed. Furthermore, the electronic circuitto which the present invention is applied is not particularly limited aslong as it has the wiring board of the single layer or multilayerstructure, the various electronic devices and electronic components, theconductor layer and insulating layer, and the like.

1. A method of manufacturing an electronic circuit having a circuitrylayer formed on a substrate having a conductor layer, comprising:exposing a photoconductor based on image information of the circuitrylayer to form an electrostatic latent image on the photoconductor;developing the electrostatic latent image on the photoconductor by tonercontaining formation material of the circuitry layer to form a tonerimage on the photoconductor; electrostatically transferring the tonerimage on the photoconductor onto the substrate so that at least a partof the conductor layer is covered, while removing excessive chargescaused in the conductor layer accompanying the start of the transfer ofthe toner image; and fixing the toner image transferred onto thesubstrate, wherein the substrate has a dummy pattern lead out from theconductor layer and the excessive charges are removed via the dummypattern.
 2. A method of manufacturing an electronic circuit having acircuitry layer formed on a substrate having a conductor layer,comprising: exposing a photoconductor based on image information of thecircuitry layer to form an electrostatic latent image on thephotoconductor; developing the electrostatic latent image on thephotoconductor by toner containing formation material of the circuitrylayer to form a toner image on the photoconductor; electrostaticallytransferring the toner image on the photoconductor onto the substrate sothat at least a part of the conductor layer is covered, while addingcharges of which polarity is reverse to that of the toner to theconductor layer; and fixing the toner image transferred onto thesubstrate, wherein the substrate has a dummy pattern lead out from theconductor layer and the charges are added via the dummy pattern.